The present invention relates generally to push buttons for switches and, in particular, to a vandal resistant push button assembly for elevator systems.
The U.S. Pat. No. 4,822,963 discloses a vandal resistant push button assembly with a push button extending through a guide ring or halo. On the operating side, the push button and the guide ring both have a spherical surface, which surface is bounded by an opening in a face plate mounting the push button assembly. The opening in the face plate is stepped from the operating side to the back or switch side, the stepwise transition forming a circular first shoulder on which the guide ring rests and on which the forces acting toward the switch are transferred to the face plate. Also disclosed is a method for the manufacture of the shoulder by means of embossing (or coining) technology instead of the customary cutting method, which has the advantage that a high mechanical strength is assured even at a relatively small thickness of the face plate.
The guide ring is designed as a tubular member with a second shoulder formed on an outer surface and a third shoulder formed on an inner surface such that the guide ring can be inserted precisely into the face plate opening with the first and second shoulders in contact where the spherical surface of the ring blends without a seam into the adjacent outer surface of the face plate. A wire shaped spring clip engages an annular groove encircling the guide ring and forms a resealable connection between the inner surface of the face plate and the guide ring. The guide ring slidably receives a push button having a fourth shoulder formed thereon for engaging the third shoulder to limit the movement of the push button in the direction of the switch. The switch is designed to bias the push button opposite to the actuation direction wherein a wire shaped spring clip engaging an annular groove encircling the push button abuts the guide ring so that the spherical surface of the push button blends without a seam into the spherical surface of the guide ring.
A disadvantage of above described push button assembly is the expensive manufacture of the face plate. In a first working step, the openings for the guide rings are punched from the face plate. A second working step is required for the embossing of the ends of the openings. Besides this, certain material thicknesses and material hardnesses are necessary for the carrying out of this process. A further disadvantage is the fact that the face plate supporting the switch assembly has to be inserted onto or into existing wall units, which impairs the aesthetic layout of the wall.